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It's A/C condensation forming on the inside of the window. As the truck shuts down, the vent control looses vacuum and sends the air to defrost, like a vacuum leak, except there isn't vacuum to keep it at the mid-vent.
No condensation. Only when I had shut the truck down this morning. I noticed the windshield fogging up.
Ok, I was wonfering if the heater core was going out
Thx, for the reply.
If it was the heater core, you'd be smelling coolant.
Next time you start the truck, while pausing for the glow plow "wait to start" light to go out, listen carefully to the truck, you should here a small clunk from the vents. Key on starts the vacuum pump, once vacuum is applied, you can hear the shift from defrost to vent.